Why my site flashes white after every click?

Hello,

You can try to temporarily deactivate all your plugins except Sydney Toolbox and Page Builder by SiteOrigin, and see if it helps.

Kind Regards, Roman.

Thank you for your response.
I deactivated all plugins, as you recommended, but the problem is still there.
Any other idea?

Okay, you can try to rebuild your website in a staging environment or locally and see if it works as it should (then you will be able to move rebuilt website to production environment). Please remember about importance of regular full site backups (files and database):
https://codex.www.ads-software.com/WordPress_Backups

Here are helpful tutorials:
https://www.wpbeginner.com/wp-tutorials/how-to-create-staging-environment-for-a-wordpress-site/
https://www.wpbeginner.com/wp-tutorials/how-to-create-a-local-wordpress-site-using-xampp/
https://www.wpbeginner.com/wp-tutorials/how-to-move-wordpress-from-local-server-to-live-site/

Kind Regards, Roman.

Finally i resolved the problem. It was the header that caused the problem. I changed the code inside the header and the white flash disappeared. Thank you for your support anyway!

Great! You are welcome ??

Kind Regards, Roman.

Hi Lengo123, what changes did you make to the header code. I have the same problem.

Hi vmdials.

I removed some code related to google analytics (google tag manager), which it was displayed at the header.
After that, everything are fine as before.
If you have still problem after that, you should check any catching plugin and of course update your theme.

Good luck!